Oursler, M and Hidler, J; National Rehab. Hospital, Washington, DC. marianne.zajacek-oursler@medstar.net.

PURPOSE: The goal of this study was to investigate how changes in walking speed and percent body-weight support (%BWS) affect muscle activation patterns and reflex excitability in individuals with spinal cord injury (SCI) during treadmill training. BACKGROUND: It has become increasingly clear that individuals with incomplete SCI who receive partial body-weight supported treadmill therapy appear to make significantly higher gains in walking ability than those who receive traditional physical therapy (Wernig and Muller, 1992, 1994). This therapy appears to effectively stimulate sensory receptors which are necessary for inducing and facilitating central pattern generators (Harkema et al., 1997). What is less clear is how changing specific training conditions, such as walking speed and %BWS, can influence the individual’s ability to execute successful stepping. We hypothesized that by optimizing these training conditions, muscle excitation and reflex excitablity would be enhanced, which in turn will lead to improved walking ability. SUBJECTS: Five individuals with incomplete SCI (ASIA C&D) participated in the study. METHODS: Each subject walked on a treadmill with robotic assistance (Lokomat, Hocoma, Inc.) at three levels of body-weight support. At each level of support, the walking speed was varied from 1.5 – 2.3 km/hr. EMG data was recorded from the soleus, tibialis anterior, rectus femoris, and hamstrings. Reflex excitability was tested by eliciting H-reflex responses in the soleus muscle at mid-stance during the gait cycle. ANALYSIS: Raw EMG data and H-reflex responses collected over a 60-second step sequence were separated into individual step cycles, and then averaged. The magnitude and timing of EMG patterns and H-reflex amplitudes were compared for each walking condition using a two-factor analysis of variance with repeated measures. RESULTS: Walking speed and %BWS each altered the amplitude and timing of EMG responses in all test subjects, however there were no consistent trends pointing to optimal walking conditions. EMG burst patterns were larger in some subjects with decreasing %BWS, however this was often associated with co-contraction of synergistic muscle groups. Similarly, increasing walking speed appeared to facilitate muscle activation patterns, however at higher walking speeds, EMG patterns deteriorated. Reflex excitability was positively correlated with increasing load (p<0.01), where H-reflex amplitudes increased with decreases in %BWS. CONCLUSIONS: Treadmill training is an effective approach to restoring walking ability in individuals with spinal cord injury, however based on the current findings, it appears that customized, per patient protocols must be implemented based on the subject’s abilities. Further testing of additional subjects is warranted to determine if there are consistent trends that would suggest optimal training conditions. FUNDING SOURCE: NRH.

Reprint Information
Requests for reprints should be directed to the corresponding author of the article. Students and other academic customers may receive permission to reprint copyrighted material from Physical Therapy by contacting the Copyright Clearance Center Inc, 222 Rosewood Dr, Danvers, MA 01923. Similar inquiries by all others should be made to the APTA Editorial Office, Attn: Physical Therapy.